Consider the Regression Equation

Consider the regression equation:
R_it- r_ft= _ai+ b_i(r_mt- r_ft) + e_it
Where:
R_it= return on stock i in month t
R_ft= the monthly risk-free rate of return in month t
R_mt= the return on the market portfolio proxy in month t
This regression equation is used to estimate

A) the security characteristic line.
B) benchmark error.
C) the capital market line.
D) all of the above.
E) none of the above.